Capillary pull alongside the weld

[keith]

Originally Posted by BTromblay

Hi,

The under cutting along your weld seam is more than likely caused by being to hot. Try an initial TIG welding setting of 1 Amp per thousand of an inch, example (.040" thick= 40amps) if in a aluminum add 10% to your current setting. For the use of filler rod in 19 gauge steel, I prefer a 1/16" diameter rod with a 1 to 1 dip rate approximately. 1to1 example (1" of filler rod for every 1" of travel).

I recommend to people that I have trained in the past, to start with a test coupon approximately 12" square, sheared in half. Weld, evaluate, shear, weld, repeat and so on. You want to verify that the heat affect zone (HAZ) / (the discoloration) is consistent and parallel to the bead and that you have full penetration on the backside. The larger coupon is used to give you a realistic result when building bigger parts. Small coupons heat up quickly and require more accurate temp control on behalf of the operator.

With practice and some basic instruction you can make a consistent weld bead that is fast, clean, full penetration and no under cutting that can be planished and fully disappear.

Let us know how you do. Hope it helps.

Bill

Bill,
That is great information. I had never thought or heard the term 1 to 1.


Thanks for the insight.


keith

[crystallographic]

When i see the diagrams of cross-sectional views of a weld on sheet, it usually looks to me as though the (heavy, thick) weld bead was made by arc welding (SMAW).
I see most students making much thinner beads in both aluminum sheet and steel sheet - using OFW and GTAW

Undercutting is caused by two things: moving the torch along too slowly, or the heat is set too high, via any torch, GTAW or OFW.

One helpful thing found when welding sheets that do Not have consistent edge thicknesses - like panels sections that have been shaped - is to modify the filler shape....
Experimentation and routine use have shown that flattening the filler (somehow) to roughly 50% of former original thickness is helpful, both in welding gaps that vary as well as thicknesses that vary - to the extent that the height of the weld bead is reduced, noticeably.

- end-

[Chris_Hamilton]

Kent, don't you always get some excessive weld on the backside when using filler? Whether it's O/A or TIG? I always have. Fusion weld with steel using O/A, I don't get any.Slight undercut on the top but from what I've seen that's normal when fusion welding. Are we talking about two different things?

[crystallographic]

Originally Posted by Chris_Hamilton

Kent, don't you always get some excessive weld on the backside when using filler? Whether it's O/A or TIG? I always have. Fusion weld with steel using O/A, I don't get any.Slight undercut on the top but from what I've seen that's normal when fusion welding. Are we talking about two different things?

"always?" um, no.
Sometimes.

Aviation inspectors specify, "Always use filler when welding, to avoid insufficient metal thickness."

Having done old auto resto, I have seen a lot of "insufficient metal thickness" on fusion welds.
In fact, used to be a body-paint outfit long ago down in Los Angeles, called "Junior's." they were very well-known for taking in brand-new Ferr. Maser. Porsche. etc etc autos, stripping off all the paint, re-welding and metal finishing all the body panels, and then painting to perfection. Friend of mine worked there doing metalwork so I got to visit and talk to Junior.
(Even made a video of a brandy-new Maser. spyder in the paint "make-ready" all stripped down and done to perfect (bare) metal work. Zero visible welds.)
Junior said "ALL" those "weld ditches" had to be re-done for the level they worked at.

It is all about "give and take" to balance out the visual requirements on the job.
When making steel sheet into bumper face bars and such, the welds cannot show through the chrome or bright nickel plate - whether GTAW or OFW.
(one advantage of resto work ... if eyeballs observant ... is studying the back side of the previous craftsmen' skills. Incalculable details lay patiently for the scrutiny. I've a 1958 TR250 factory orig hood scoop, zero damage, stripped gently to reveal a virtual encyclopaedia of technique, style, low-production finesse and "Scaglietti race" quality. Some edges have the factory paint/primer layers - meaning this car had the factory original finish - never re-coated.

Some welders work at the fine point elements to make exact-thickness welds.
One element is using precise fits.
Another is fine-dimension filler.
Precise heats.
+ Ummm ... steady hand?

I've seen some mighty fine welds .....